1. Field of the Invention
The present invention relates to electrostatic printers and more particularly to a high speed electrostatic color printer.
2. Description of the Prior Art
Numerous electrostatic printers, both black and white and color, are known in the art. These printers may use processes in which a latent electrostatic image is formed on a photoconductive surface, toned, physically moved and electrostatically transferred to the contacting print medium. Other processes utilize an array of electrodes to write a latent image on a dielectric surface, in place of the photoconductive surface. Direct electrostatic transfer of toner is also used in some of the processes of the prior art. However, none of the prior art printing systems have integrated logic, memory, and imaging capabilities into a single functional element. Nor have effective toner delivery systems been described for color printed systems of this type.
U.S. Pat. No. 3,689,935, issued to Pressman et al., has described a multi-layered particle modulator which utilizes a linear array of apertures to modulate the density of a charged particle stream. The modulated stream can include direct marking toner particles, or may comprise ions which form a latent image on the receiving print medium which is subsequently dusted and developed according to known techniques. Thompson, U.S. Pat. No. 4,068,585, describes a similar apparatus using a multi-layered particle modulator to modulate an ion stream. Focusing of the particles, in both patents, is achieved using the imaging apertures of the modulator. Kilby et al., U.S. Pat. No. 3,979,758, describes an electrostatic write head implemented with integrated circuit technology and employing low voltage binary circuits. U.S. Pat. No. 4,338,615, issued to Nelson et al., discloses an apparatus and method for printing on plain paper utilizing a solid-state write head and electrostatic imaging. An LED array is used to selectively discharge a photoconductive belt, and charge is directly transferred from the belt to the receiving print medium. U.S. Pat. No. 4,356,501, issued to Ronen, describes an integrated silicon nib for an electrostatic printer.
In view of the prior art, there remains a need for a mechanically simple electrostatic color printer capable of printing images in multiple colors, made up of a plurality of pixels, the color density of each of which can be varied, and printing such images in a single pass of the print medium past the writing head.